Tool "ejector"

Help! My collet set is ejecting tools, and I cannot keep them in. I'm trying to hold a 1" end mill and cut a long slot. The cut ends up being about .150 deeper per inch. I have cleaned the collet and mill in acetone, lubed the collet holder taper and threads making sure not to get oil on the inside of the collet, tightened it until the wrench broke, made a new and improved wrench, tightened some more, and still have problems. There is no chatter, just a nice smooth cut, running 900 RPM with .0025 chip load. If I keep the cut less than .250 deep, it does OK.

I've already ruined a big piece of 4140, and chipped my $130 cutter

The collet set IS a chinese set I got on ebay, but I was pleased with them until I had to do any heavy cutting. Runout is good, everything is clean and not damaged. What can I do?

Just some ideas here ...

1. Tram your mill in.

2. Check your collet for galling.

3. Check your spindle bore for trash.

4. Check your cutter shank for taper.

5. Check the angles on the collet and spindle ... do they match?

6. Lok-tite that baby in the collet.

7. Get another collet.

The first 5 may not cause your problem on light cuts but become progressively worse under increasing loads.

Well, there's no mystery, really, the large forces owing to positive rake are pulling the cutter out of the holder just like you said.

Switch to a setscrew-style holder. 1" endmill holder has 2 healthy-sized setscrews that should solve the problem. Assuming this is a carbide cutter with no Weldon flats, you may choose to grind a pair of flats.

Regards.

Finegrain

Slotting is one of the most labor-intensive applications of a milling machine, because you have cutting engagement over half of the tool's circumference. What collet taper?

You seem to know what you're doing (calculated chip per tooth) but I'm wondering if you're trying this with a small machine and weak taper that won't provide enough clamping force.

more than .250 with a 1" EM in 4140... now that I want to see working (especially at the far end where the EM is pulled down .150 more)!

Good Luck,
Henry Wettersten